1. Field of the Invention
The present invention relates to a liquid crystal display device and more particularly, to a liquid crystal display device and a method of manufacturing the same capable of reducing the number of processes by forming a light shielding layer through the use of a mask process used to form a spacer.
2. Discussion of the Related Art
Recently, with an increasingly information-oriented society, a flat panel display device is needed that is light, thin and has low power consumption. Among the flat panel display devices, liquid crystal display devices have excellent resolutions, color displays and picture qualities, etc. Thus, liquid crystal display devices are used in notebook monitors or desktop monitors.
In general, the liquid crystal display device includes two substrates, each of which has an electrode formed at one side thereof. The two substrates are arranged so that the surfaces having the electrodes face each other. A liquid crystal material is injected between the substrates. After that, an electric field generated when a voltage is applied to the electrodes causes movement of a liquid crystal molecule. Accordingly, a transmittance of light becomes different, to thereby display a picture.
A lower glass of the liquid crystal display device is employed as an array substrate including a thin film transistor for applying a signal to a pixel electrode, and is formed by repeatedly making a thin film and performing photolithography and etching with respect to the thin film. An upper glass of the liquid crystal display device is employed as a substrate including a common electrode and a color filter. The color filter includes three colors of red R, green G and blue B which are sequentially arranged on the upper glass.
Such a liquid crystal display device is made by a sequential process of separately forming a thin film transistor array substrate and a color filter array substrate, and arranging the pixel electrode of the thin film transistor array substrate and the color filter of the color filter array substrate to correspond with each other in a one-to-one relationship. However, misalignment occurs during the process of arranging the substrates, which causes problems such as light leakage. In order to prevent these problems, the upper glass may be made to have a black matrix with a wide width. However, in this case, an aperture ratio of the liquid crystal display device is lowered.
Thus, in order to prevent the misalignment of the liquid crystal display device and improve the aperture ratio, a method of forming the color filter on the thin film transistor array substrate has been proposed recently. The color filter on an upper thin film transistor is referred to as a color filter on thin film transistor (COT) structure.
FIG. 1 is a sectional view illustrating a liquid crystal display device having a related art COT structure.
As shown in FIG. 1, a gate electrode 12 made of a conductive material such as a metal is formed on a first transparent substrate 11. The gate electrode 12 is covered by a gate insulating film 13 made of silicon nitride (SiNx) or silicon oxide (SiO2) on the gate electrode 12.
An active layer 14 made of amorphous silicon is formed to be overlapped with the gate electrode 12 on the gate insulating film 13. An ohmic contact layer 15 made of amorphous silicon having a doped impurity is formed on the active layer 14.
A source electrode 16a and a drain electrode 16b made of conductive materials such as metals are formed on an upper portion of the ohmic contact layer 15. The source electrode 16a and the drain electrode 16b along with the gate electrode 12 constitute a thin film transistor T.
Meanwhile, the gate electrode 12 is connected to a gate line (not shown), the source electrode 16a is connected to a data line (not shown). The gate line and the data line cross each other, to thereby define a pixel region.
A first passivation film 17, which is made of silicon nitride, silicon oxide or an organic insulating film, is formed on an entire surface of the first substrate 11 including the source electrode 16a and the drain electrode 16b. The first passivation film 17 is used for protecting the thin film transistor T.
A black matrix 22 is formed at a location corresponding to the thin film transistor T, on the first passivation film 17. The black matrix 22 has an aperture at a portion corresponding to the pixel electrode 20 and is formed on an entire surface of the substrate. Thus, the black matrix 22 prevents light leakage resulting from tilting of the liquid crystal molecule at a portion besides the pixel electrode. Further, the black matrix 22 shields light incident to a channel portion of the thin film transistor T to prevent generation of a light leakage current.
A color filter 18 is formed at the pixel region on the first passivation film 17. In the color filter 18, red, green and blue colors are arranged in sequence, and each color corresponds to one pixel region. The color filter 18 is formed at a portion corresponding to the drain electrode 16b to be exposed via a contact hole 19. A second passivation film 13 made of an inorganic insulating film such as silicon oxide or silicon nitride, or an organic insulating film such as an acrylic system resin or BCB (benzocyclobutene) is formed on the color filter 18. The second passivation film 24 serves to prevent the liquid crystal material from being contaminated by the color filter 18.
A contact hole 19 is formed to pass through the second passivation film 24 and the first passivation film 17 to expose the drain electrode 16b. The pixel electrode 20 electrically connected to the drain electrode 16b via the contact hole 19 is formed at the pixel region of the second passivation film 24, wherein the pixel electrode is made of a transparent conductive material. Also, a spacer 25 is formed at a portion corresponding to the thin film transistor T, on the second passivation film 24.
Meanwhile, a second transparent substrate 21 is arranged on an upper portion of the first substrate 11 and is separated from the first substrate 11 by a defined distance by the spacer 25. A common electrode 23 made of a transparent conductive material is formed on the second substrate 21.
The first substrate 11 is combined with the second substrate 21, and a liquid crystal layer 30 is injected between the pixel electrode 20 and the common electrode 23. An array state of the liquid crystal molecule of the liquid crystal layer 30 is changed by an electric field generated when a voltage is applied to both the pixel electrode 20 and the common electrode 23. An alignment film (not shown) is formed at each of an upper portion of the pixel electrode 20 and a lower portion of the common electrode 23, to thereby determine an initial array state of the liquid crystal molecule.
As set forth above, the color filter 19 is formed on the same first substrate 11 (i.e., the lower glass) on which the thin film transistor T is formed, to thereby prevent misalignment of the color filter 18 and the pixel electrode 20 when the first substrate is combined with the second substrate 21 (i.e., the upper glass). Thus, even though the black matrix 22 is not wide, the aperture of the liquid crystal display device can be improved.
FIGS. 2A to 2F are sectional views illustrating a method of fabricating the array substrate for the related art liquid crystal display device.
Referring to FIG. 2A, a metallic material is deposited on the first substrate 11 and is patterned by way of photolithography, to thereby form the gate electrode 12. When the gate electrode 12 is formed, a gate line (not shown) connected to the gate electrode 12 and extending in a first direction is also formed along with the gate electrode 12.
Silicon nitride or silicon oxide is deposited on an entire surface of the first substrate 11 so as to cover the gate electrode 12, to thereby form the gate insulating film 13. Also, an amorphous silicon layer and an amorphous silicon layer doped with an impurity are sequentially deposited on the gate insulating film 13. And then, the active layer 14 and the ohmic contact layer 15 are formed by patterning by way of photolithography so that the active layer 14 and the ohmic contact layer 15 overlap the gate electrode 12 and overlap at least a portion of the source electrode 16a and a partial drain electrode 16b through a width wider than the gate electrode 12.
Referring to FIG. 2B, a metallic material is deposited on an entire surface of the first substrate 11 and then is patterned by way of photolithography, to thereby form the source electrode 16a and the drain electrode 16b. When the source electrode 16a and the drain electrode 16b are formed, the data line (not shown) defining the pixel region along with the gate line is also formed. The data line is connected to the source electrode 16a and extends in a second direction crossing the gate line. At this time, the ohmic contact layer 15 between the source electrode 16a and the drain electrode 16b is patterned and then is removed.
The source electrode 16a and the drain electrode 16b along with the gate electrode 12 constitute the thin film transistor T.
Referring to FIG. 2C, an inorganic insulating film such as silicon oxide or silicon nitride is deposited, or an organic insulating film such as an acrylic resin is coated, on the source and the drain electrodes 16a and 16b, to thereby form the first passivation film 17.
A black matrix material is deposited on the first passivation film 17 and then is patterned by photolithography and etching, to thereby form the black matrix 22. A photosensitive material capable of filtering red R, green G and/or blue colors is applied to the first passivation film 17 and then is patterned by an exposure process and a developing process, to thereby form the color filter 18 at the pixel region including the transistor T. The color filter 18 includes red, green and blue colors, so that the procedure of applying, exposing and developing is repeated three times. Thus, a color filter 18 representing each color can be formed. The color filter 18 is formed at a portion corresponding to the drain electrode to be exposed via the contact hole 19.
Referring to FIG. 2D, an inorganic insulating film such as silicon oxide or silicon nitride is deposited, or an organic insulating film such as an acrylic resin or a BCB (benzocyclobutene) is coated, on the color filter 18, to thereby form the second passivation film 24.
And then, the first and the second passivation films 17 and 24 are sequentially patterned by way of photolithography, to thereby form the contact hole 19.
Referring to FIG. 2E, a transparent conductive material is deposited on the second passivation film 24 and then is patterned by way of photolithography, to thereby form the pixel electrode 20. The pixel electrode 20 corresponds to the color filter 18 in a one-to-one relationship and is electrically connected to the drain electrode 16b via the contact hole 19.
Thereafter, a spacer 25 made of a resin is formed at a portion corresponded to the thin film transistor T on the second passivation film 24. A resin is applied to the second passivation film 24 and the pixel electrode 20 and then is exposed and developed to remain at a portion corresponding to the thin film transistor T, to thereby form the spacer 25.
The thin film transistor T, the color filter 18 and the pixel electrode 20 are formed on the first substrate 11, to thereby complete the lower array substrate of the liquid crystal display device.
Referring to FIG. 2F, a transparent conductive metal is deposited on an entire surface of the second substrate 21, to thereby form the common electrode 23.
The common electrode 23 is formed on the second substrate 21, to thereby complete the upper array substrate.
Although not shown in FIG. 2, the upper glass is combined with the lower glass, and the liquid crystal material is injected into a space formed by the spacer 25, to thereby form the liquid crystal layer 3.
However, the above-mentioned liquid crystal display device requires a separate photolithographic process for forming the black matrix so that the channel portion of the thin film transistor T is not exposed to light. Further, the black matrix is overlapped with at least one of the gate line, the data line and the thin film transistor T with the first passivation film 17 therebetween, to thereby result in a parasitic capacitor. The parasitic capacitor has a relatively high capacitance as the first passivation film 17 is made of an inorganic insulating material having a high dielectric constant, which distorts a gate signal supplied to the thin film transistor T via the gate line and a data signal supplied to the thin film transistor T via the data line.